In general, an encoder is a device that detects a displacement, a rotation direction, and an angle. The encoder is also used for a vehicle, and the encoder is installed on a bearing device so as to detect the number of revolutions and a rotation direction of a wheel.
FIG. 1 is a cross-sectional view of a magnetic encoder, and FIG. 2 is an exploded perspective view of a wheel speed measuring device in the related art.
Referring to FIGS. 1 and 2, the magnetic encoder serves to transmit a rotation speed of a wheel to a sensor. The magnetic encoder includes iron oxides that are magnetized to N/S poles on rubber. The N poles and the S poles are repeatedly disposed in a ring shape.
The magnetic encoder 16 is coupled to one surface of a wheel bearing 14, and rotated together with the wheel bearing 14 when the wheel bearing 14 is rotated. An ABS sensor 12 is positioned on a rear surface of the magnetic encoder 16, and the ABS sensor 12 senses the rotation of the magnetic encoder 16.
In general, regarding the magnetic encoder 16, there are an encoder ring type magnetic encoder that is configured separately and press-fitted into a rotating wheel of the wheel bearing 14, and an encoder seal type magnetic encoder that is configured integrally with a bearing seal rubber by magnetizing an iron oxide on the bearing seal rubber.
When the magnetic encoder 16 in the related art is used, magnetic density of the magnetized encoder needs to be high in order to obtain a stable electric current value in a wheel sensor. An area of the encoder is an important factor in increasing the magnetic density, and the magnetic density is increased as areas of portions, where the encoder is magnetized to the N poles and the S poles, become larger. Therefore, in the case of the encoder ring type magnetic encoder and the encoder seal type magnetic encoder, a radius of the encoder needs to be a predetermined value or more in order to satisfy target sensitivity of the sensor.